@article{oai:repository.dl.itc.u-tokyo.ac.jp:00039676,
 author = {Ishihara, Koichiro},
 issue = {1},
 journal = {Journal of the Faculty of Science, the University of Tokyo. Sect. 1 A, Mathematics = 東京大学理学部紀要. 第1類A, 数学},
 month = {Mar},
 note = {application/pdf},
 pages = {167--181},
 title = {A new characteristic number for almost free $T^2$-actions},
 volume = {26},
 year = {1979}
}